Among 70 victims of sudden coronary death (SCD), certain clinical and morphologic findings in the 13 with a coronary thrombus are compared with the findings in 57 victims without a coronary thrombus. Compared to those without, the 13 with a thrombus were younger (mean age 43 - vs - 51 years, p = Less than 0.02); had a lower mean percent of cross-sectional area (XSA) narrowing by plaque at the site of maximal coronary stenosis (89% - vs -95%, p = Less than 0.01); and had a higher mean percent of 5-mm segments of the 4 major epicardial coronary arteries minimally narrowed (0-25% in XSA) by plaque (27% - vs - 19%, p = Less than 0.001). No differences occurred in the 2 groups with regard to sex, previous angina pectoris and/or clinical acute myocardial infarction, healed myocardial infarction at necropsy, mean heart weight, number of major coronary arteries narrowed 76-100% in XSA by atherosclerotic plaque, or the mean percent of 5-mm segments of the 4 major epicardial coronary arteries narrowed 76-100% in XSA by atherosclerotic plaque. Thus, coronary thrombi are infrequent in victims of SCD, and when observed, their significance is uncertain because victims of SCD without coronary thrombi have similar amounts of severe coronary narrowing.